Magnetic material



June 4, 1929.

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G. w. ELMEN MAGNETIC MATERIAL Filed June 28, 1928 F/al 6 l/VVENTUR80574; W ELME ATTORNEY Patented J une 4 4, 1929 UNITED STATES GUSTAF W.ELMEN, OF LEONIA, NEW JERSEY, ASSIGNOR TO BELL TELEPHONE LAB- ORATORIES,INCORPORATED, 015' NEW YORK, N. Y., A CORPORATION OF NEW YORK.

'MAGNETIG Application filed June 2 The present invention relates tomagnetic materials and to their application in electromagnetic systems;Materials in accordance with the present invention have a field ofusefulness and are of special interest in those cases in which theimpressed magnetizing forces are small such as in electric signalingsystems. More particularly, the present invention relates to magneticcompositions 10 having a relatively low hysteresis lossand a high degreeof constancy of permeability for magnetizing forces up to several gauss.In Elmens applications Serial No. 119,622 and Serial No.-119,623,both'filed June 30, 1926, there are described and claimed magneticcompositions of iron, nickel and cobalt which have been discovered tohave, among other unusual properties, a very high degree of constancy ofpermeability over a Wide range ofmagnetizing forces including the lowrange employed in loadingsignaling conductors. a

The utility of such compositions may be increased, especially forapplicationswhere low eddy current loss is' desirable, by increasingtheir resistivity, when this can be done without excessivelyorconsiderably im-. pairing their other desirable properties. In Elmenapplication Serial No. 220,387, filed September 19, 1927 there aredescribed and claimed several compositions having their resistivityincreased, and other properties improved or modified adversely to aslight extent only by the addition of moderate per.- centages of suchelements as molydenum, chromium, tungsten, manganese, vanadium,tantalum, zirconium, copper and silicon.

Among such iron-nickel-cobalt compositions is noted a genus or varietyin which the permeability remains constant or very nearly so formagnetizing forces as high as four gauss, more or less. Thesecompositions, which in general are characterized also by a moderatelylow initial permeability and a cobalt content of more than 45 per cent(in most cases) of the entire iron-nickelcobalt content, constitute asubject matter of the present invention. These compositions have a fieldof usefulness where constancy of permeability for considerablemagnetizing forces is desired, for example, in loading coils forsignaling conductors.

The resistivity of such high cobalt com- MATERIAL.

1928. Serial No. 289,050.

positions may be increased by the addition of one or more of the fourthsubstances mentioned above in moderate amounts, and such compositionshaving increased resistivity constitute another feature of the presentout limitation of their cobalt content to ahigh value.

In order to develop desirable properties in compositions such as claimedherein or to accentuate certain properties, particular heat treatmentshave been found to be desirable, These treatments differ for differentcompositions, and While the particulartreatment'best suited for aparticular composition may be selected. in accordance with thedirections below, one heat treatment which was productive ,ofsatisfactory initial permeabilities, good constancies of permeabilityand small hysteresis losses, whenever used, will now be described,

The magnetic compositions, after having been prepared by melting theingredients together in the proper proportions in an induction furnace,were allowed to cool and tained at that temperature for about one hourand then cooled at such a rate that at each degree of coolingtemperature the material was in a condition of equilibrium, that is,that no changes in itsstructure took place. For the various compositionsdescribed in this application, a suitable rate of cooling was found toconsist in cooling within the furnace at approximately 200 C. per hourfor the first hour, 100" C. for the next two hours, 66% C. per hour forthe next three hours, 50 C. for the next four hours 'and 40 C. per hourfor the remainder of the time required to reach room temperature. Thistreatment will be referred to herein as heat treatment I.

Another suitable method consists in heating the materials to about 11000., cooling to room temperature, reheating to about 435 C., maintainingthem at that temperature for about 40v to 60 hours and then cooling themslowly at an average rate. of about 50 C. per hour to room temperature.The most favorable length of time for which the materialshould be heatedat about 435 C. varies somewhat for difierent compositions, but canreadily be determined by a few tests. u

The curve of Fig. 1 shows the. measured variation of permeability withvarying magnetizing force of a virgin alloy containing approximately 16per cent iron, 30.5 per cen nickel, 50 per cent cobalt, 3.5 per centmolybdenum, having received heat treatment I.

This material exhibited an initial permeability of 113,- which remainedpractically constant up to a magnetizing force of about 4 gauss. It hada resistivity of about 47.6 microhm-cms. and a hysteresis loss of 4490ergs percycle per cubic centimeter for a maximum induction of 7400gauss.

Fig. 2 depicts the measured variation of permeability with a varyingmagnetizing force for a composition containing 20 per cent iron, 10 percent nickel and per cent cobalt given heat treatment I. The initialpermeability was about 57 and remained constant up to magnetizing forcesof over 4 gauss. One half a hysteresis curve of this particularcomposition is shown in Fig. 3; it is seen stantially zero up to theflux density of about gauss.

The curve of Fig. 4 graphically shows the measured variation ofpermeability with varying magnetizing force for a composition containing17 per cent iron, 26 per cent nickle, 55 percent cobalt and 2 per centtitanium after having received heat treatment I. The initialpermeability, which was about 90 remained substantially constant withincreasing magnetizing force up to about 5 gauss. The maximumpermeability which occurred at about 10 gauss magnetizing force was 9200and the resistivity about 30 microhm-cms. The hysteresis loss of thismaterial was 7500 ergs per cubic centimeter per cycle for a maximuminduction of .8000 gauss and its coercive force and remanence were 5.27and .7720 gauss respectively for a maximum induction of 13000.

In Fig. 5 is shown the measured variation of permeability withincreasing magnetizing force of a composition containing. ap-

proximately 28 per cent iron, 45 per cent nickel, 26'per cent cobalt and1 per cent titan- 111m after being given heat treatment I. Thiscomposition had an initial' permeability of about 345whichremained'constant up to about 1.5 gauss. Its maximum permeabilitywas about 1850 and its restivity 30 microhmcms. Its hysteresis loss was1795 ergs per permeability 20 per cent cent cobalt and 0.3 per centmanganese, given and a trace of manganese, after that the hysteresisloss was sub-.

cubic centimeter per cycle fora maximum induction of 7500 gauss. It hada coercive force of 1.17 and a remanence of 2735.

Fig. 6 shows the measured variation -of with increasing. magnetizingforce of a material containing approximately iron, 20 per cent nickle,60 per heat treatment I. This material had an initial permeability ofabout 50 which remained constant up to a magnetizing force of about 4gauss. Its maximum permeability which occurred at about 6 gauss was1200. The material had a hysteresis loss of 7440 ergs per cubiccenetimeter percycle for a maximum induction of 16,000 gauss. Its 00-ercive force was 2.60 gauss and its remanence 3,820 gauss for a maximuminduction of 14,200 gauss.

In distinguishing between compositions having constancy of permeabilityfor high flux densities combined with relatively high initialpermeability and those of lower initial permeability constant to ahigher mag: netizing force the dividing line has been setat the pointwhere cobalt constitutes about 45 per cent of the iron-nickel-cobaltcontent.

This is' based as nearly as possible upon physical difi'erences in thecompositions having over 45 per cent and those having less than 45 percent cobalt. However, the dividing line is not an exact one and variessomewhat with the percentage of nickel. Thus with compositions 01510 percent nickel and varying proportions of cobalt and iron 21. great changein properties takes place in passing from 30 per cent to 40 per centcobalt. The flux density B, for H=50-increases from 7000 to over16000and the hys teresis loss for a loop B=5000 maximum decreasesenormously as the cobalt content is increased from 30 to 40 per cent andthe iron decreased from 50 per cent to 40 per cent. With compositions of20 per cent nickel, however, corresponding but less striking changesoccur as the cobalt content is increased through about50 per cent. Thesefacts are cited as evidence that a more or leSS distinct genus of heattreated magnetic ironnickel-cobalt compositions comprises those havingabove about 45 per cent cobalt.

Although the present invention has'bec n described with particularreference to but titanium and molybdenum as fourth elements in, magneticcompositions containing ,Serial No. 220,387, filed September 19, 1927may be used in amounts of 1 per cent to several per cent, 'e1ther singlyor in combination. More specifically, any of the fourth elementsmentioned may be substituted for the molybdenum or titanium content ofthe compositions hereinbefore described.

What is claimed is:

1. A magnetic composition composed chiefly of iron, nickel, and cobaltincluding 9 per cent or more of iron, 4 per cent or more of nickel, andcobalt, with or without the addition of a fourth substance to increasethe resistivity or modify the other properties, characterized by acobalt con'lent greater than 45 per-cent of the iron-nickelcobaltcontent and not in excess of,80 per cent of the entire composition.

2. A magnetic material containing as essential constituents thereofnickel, cobalt and iron in which the cobalt content is greater than 45per cent of the total nickel-cobaltiron content and in which the threeelements named constitute the major portion of the iron content and lessthan 85 per cent of the entire composition.

4. A magnetic material characterized by a negligible variation inpermeability over a wide range of magnetizing forces compris ing nickelmore than 5 per cent, iron more than 9 per cent, and cobalt more than 45per cent,

5. A magnetic composition comprising nickel approximately 30 per cent,cobalt approximately 50 per cent and the balance chiefly iron.

6. A magnetic composition comprising nickel approximately 30 per cent,cobalt ap proximately 50 per cent and the remainder composed chiefly ofiron plus material selected to include material chiefly of the followingelements, molybdenum, chromium, tungsten, manganese, vanadium, tantalum,zirconium, copper, silicon and titanium.

, A magnetic composition containing as essential elements thereofnickel, cobalt, iron and titanium in which the cobalt content is greaterthan 40 per cent of the total of nickel, at least 5 per cent of cobaltandtitanium to an extentgreater than an incidental impurity and lessthan 10 per cent.

In witness whereof, I hereunto subscribe my name this 27th day of June,1928.

GUTAF W. ELMEN;

